The alternating, layer-by-layer adsorption of positively and negatively charged polymers on surfaces is a convenient and versatile method for the fabrication of well-defined, nanostructured thin films. The stepwise nature of this process permits precise control over the compositions, thicknesses, and surface properties of multilayered assemblies fabricated from a wide variety of water-soluble polymers. The ability to incorporate biologically-active species such as peptides, proteins, and DNA into these assemblies without loss of biological function has made possible the development of catalytically- and biologically-active thin films, membranes, and microcapsules with potential applications in many areas of biology, biotechnology, and medicine (Lynn, 2006, Soft Matter 2: 269-273).
Past work describing the incorporation of proteins into multilayered polyelectrolyte assemblies has focused largely on naturally occurring (that is, wild-type) proteins. Manipulating the pH or ionic strength of polyelectrolyte, protein, or polypeptide solutions used during fabrication, can influence the growth and structures of these films as well as the structure and function of incorporated proteins. One general limitation of this approach, however, is that assembly conditions and film properties are often dependent upon the magnitude and sign of the net charge, isoelectric point, and other physical properties of the native proteins or polyelectrolytes that are used. Model peptides rationally designed to contain high densities of cationic residues (e.g., lysine) or anionic residues (e.g., glutamic acid) can be used to facilitate the assembly of multilayered films using layer-by-layer procedures (Li and Haynie, 2004, Biomacromolecules 5: 1667-1670).